BIOL 2420 Study Guide: Muscle, Cardiovascular, and Blood Physiology

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Muscle Physiology

Structural Features of Skeletal Muscle

Skeletal muscle fibers are specialized cells responsible for voluntary movement. Understanding their structure is essential for grasping how muscles contract and generate force.

Muscle Fiber: The basic cellular unit of skeletal muscle, also called a myofiber.
Myofibrils: Cylindrical structures within muscle fibers, composed of repeating units called sarcomeres.
Sarcomere: The functional contractile unit of muscle, defined by Z lines. Contains thick (myosin) and thin (actin) filaments.
Other Structures: T tubules (transverse tubules), sarcoplasmic reticulum (SR), mitochondria, glycogen granules.

Example: The sliding filament model describes how actin and myosin filaments slide past each other to shorten the sarcomere during contraction.

Mechanism of Muscle Contraction

Muscle contraction is initiated by an action potential and involves a series of biochemical events known as the crossbridge cycle.

Excitation-Contraction Coupling: The process linking muscle fiber excitation to contraction via Ca2+ release from the SR.
Crossbridge Cycle: Myosin heads bind to actin, perform a power stroke, detach, and reset. ATP is required for detachment and re-cocking of the myosin head.
Role of Calcium: Ca2+ binds to troponin, causing tropomyosin to move and expose binding sites on actin.

Key Steps:

Action potential travels down T tubule.
Ca2+ released from SR.
Ca2+ binds troponin; tropomyosin shifts.
Myosin binds actin; power stroke occurs.
ATP binds myosin; crossbridge detaches.

Example: Rigor mortis occurs when ATP is depleted, preventing crossbridge detachment.

Types of Skeletal Muscle Fibers

Skeletal muscle fibers are classified based on their contraction speed and metabolic properties.

Slow Oxidative (Type I): Fatigue-resistant, high endurance, rich in mitochondria.
Fast Oxidative-Glycolytic (Type IIa): Intermediate properties.
Fast Glycolytic (Type IIb): Rapid, powerful contractions, fatigue quickly.

Example: Marathon runners have more Type I fibers; sprinters have more Type IIb fibers.

Cardiovascular System: Cardiac Function

Cardiac Cycle and Heart Sounds

The cardiac cycle describes the sequence of events in one heartbeat, including changes in pressure and volume in the heart chambers.

Systole: Contraction phase; blood is ejected from ventricles.
Diastole: Relaxation phase; ventricles fill with blood.
Heart Sounds: "Lub" (S1) from AV valve closure; "Dub" (S2) from semilunar valve closure.

Example: Blood pressure is highest during ventricular systole.

Electrical Activity of the Heart

The heart's rhythmic contractions are coordinated by its electrical conduction system.

SA Node: Pacemaker; initiates action potentials.
AV Node: Delays impulse, allowing ventricular filling.
Bundle of His, Bundle Branches, Purkinje Fibers: Distribute impulse through ventricles.

Electrocardiogram (ECG): Records electrical activity; P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

Cardiac Output

Cardiac output (CO) is the volume of blood pumped by each ventricle per minute.

Formula:

HR: Heart rate (beats per minute)
SV: Stroke volume (volume per beat)

Example: If HR = 70 bpm and SV = 70 mL, CO = 4900 mL/min.

Cardiovascular System: Blood Vessels, Blood Flow, and Blood Pressure

Blood Vessel Structure and Function

Blood vessels transport blood throughout the body and are classified by structure and function.

Arteries: Carry blood away from the heart; thick, elastic walls.
Veins: Return blood to the heart; thinner walls, valves prevent backflow.
Capillaries: Site of exchange between blood and tissues; thin walls for diffusion.

Blood Pressure and Flow

Blood pressure is the force exerted by blood on vessel walls. Blood flow depends on pressure gradients and resistance.

Mean Arterial Pressure (MAP): Average pressure in arteries during one cardiac cycle.
Formula:

TPR: Total peripheral resistance

Example: Vasoconstriction increases TPR and MAP.

Cardiovascular System: Blood

Blood Components and Functions

Blood is a connective tissue with several components, each with specialized functions.

Plasma: Liquid matrix; transports nutrients, hormones, waste.
Red Blood Cells (Erythrocytes): Carry oxygen via hemoglobin.
White Blood Cells (Leukocytes): Immune defense.
Platelets (Thrombocytes): Blood clotting.

Hematopoiesis and Erythropoiesis

Blood cells are produced in the bone marrow through hematopoiesis. Erythropoiesis is the specific process of red blood cell formation.

Key Steps: Stem cell → erythroblast → reticulocyte → erythrocyte.
Regulation: Erythropoietin (EPO) from kidneys stimulates RBC production in response to hypoxia.

Example: High altitude increases EPO secretion, raising RBC count.

Hemostasis

Hemostasis is the process of stopping bleeding, involving vascular spasm, platelet plug formation, and coagulation.

Platelet Plug: Platelets adhere to damaged endothelium and aggregate.
Coagulation Cascade: Series of enzymatic reactions leading to fibrin clot formation.
Key Factors: Thrombin, fibrinogen, fibrin, prothrombin, calcium ions.

Respiratory System: Pulmonary Ventilation and Gas Exchange

Pulmonary Ventilation

Pulmonary ventilation is the movement of air into and out of the lungs, driven by pressure changes.

Inspiration: Diaphragm contracts, thoracic volume increases, pressure decreases, air flows in.
Expiration: Diaphragm relaxes, thoracic volume decreases, pressure increases, air flows out.

Example: During exercise, both rate and depth of breathing increase.

Gas Exchange and Transport

Gas exchange occurs in the alveoli by diffusion, driven by partial pressure gradients.

Oxygen Transport: Mostly bound to hemoglobin; small amount dissolved in plasma.
Carbon Dioxide Transport: Dissolved in plasma, bound to hemoglobin, or as bicarbonate ion (HCO3-).

Formula:

Example: Hyperventilation decreases CO2 and raises blood pH.

Summary Table: Types of Muscle Fibers

Type	Contraction Speed	Fatigue Resistance	Major Pathway
Type I (Slow Oxidative)	Slow	High	Oxidative phosphorylation
Type IIa (Fast Oxidative-Glycolytic)	Fast	Intermediate	Oxidative & Glycolytic
Type IIb (Fast Glycolytic)	Fast	Low	Glycolysis

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Key terms and processes were defined to ensure the notes are self-contained.